Methods for making random yarn denier variations are known in the art. Variable denier yarns of synthetic polymers are useful in providing the means of producing variable texture and dying effects in the fabrics made therefrom. Thus, mottled or other novelty effects can be produced when the fabric is dyed with a given dye stuff owing to the varying rates and extents to which the dye stuff is taken up by the portions of different deniers.
Drawing is a process typically used on synthetic yarns. Virtually all synthetic filament yarns are drawn to provide for molecule orientation within the yarn. There are three conventional or draw twisting types of drawing. In the first method, known as spin drawing, each individual synthetic filament is drawn during the spinning process. The second method is termed draw warping and is used in weaving or warp knitting. Here, multiple filaments are drawn collectively in parallel side-by-side relation in the form of a sheet of filaments. In the third, each individual synthetic filament is drawn individually in a process separate and apart from the spinning process.
Previous methods have shown that irregularity or unevenness in the fiber thickness of individual filaments can be formed in synthetic filaments during spin drawing by changing the extrusion amount, the take-up speed, the spun length or the spinning atmosphere in the spinning step, or by changing the spin draw ratio, the spin drawing zone length or the spin drawing atmosphere in the drawing step. U.S. Pat. No. 4,147,749 to Lipscomb et al discloses a method for producing fibers during spin drawing from synthetic polymeric materials having randomly produced sections of high and low orientation and varying cross section areas. The varied orientation and cross section areas are produced by quickly cooling the fiber and drawing the fiber below its natural draw ratio.
The known methods of draw-induced denier variations are performed only during spin drawing, not draw warping. Inducement of denier variation on the draw warping process has not been tried or accomplished because it is important that the denier randomness vary not only along the length of each filament but also laterally across the length of the warp sheet from one filament to the next. Thus, since the draw warping process treats the same lengthwise point of each filament at the same time, it would be expected that draw-induced denier variations performed during draw warping would not accomplish the goal of random variations from filament to filament but, instead, produce variations at the same lengthwise points in each filament. Thus, no method for producing random yarn denier variations in draw warping machines has been developed.